When a site is slow to load, most visitors don’t wait. They close the tab and move to the next result. That decision happens within a few seconds — and it costs you clients you’ll never even know about.
This isn’t a marginal problem. It’s one of the most common issues on Luxembourg business websites, and one of the least visible to the site owner, who typically checks it over WiFi from their desk, on desktop, with the site already cached.
What slowness actually does
A visitor arriving on your site from Google has no obligation to be patient with you. If the page loads too slowly, they go back to the results and click on the next one.
According to Google’s public data (Find out how you stack up to new industry benchmarks for mobile page speed), the probability that a visitor leaves the site rises by 32% when load time goes from 1 to 3 seconds, and by 90% when it goes from 1 to 5. This behaviour is systematic on mobile, where connections are sometimes less stable and users expect an immediate response.
Slowness has two compounding effects: it drives away visitors who arrive on your site, and it degrades your ranking in Google’s results. Since 2021, Google has incorporated Core Web Vitals into its official ranking criteria.
A slow site is therefore less visible and less effective at the same time.
Core Web Vitals: what Google actually measures
Three metrics make up the official Core Web Vitals:
- LCP (Largest Contentful Paint): time before the largest visible element renders. Target: under 2.5 seconds.
- INP (Interaction to Next Paint): responsiveness to user interactions (click, scroll). Target: under 200 ms. Replaced FID in March 2024.
- CLS (Cumulative Layout Shift): visual stability during page load. Target: under 0.1.
These three metrics are measured under real conditions on actual users’ devices (CrUX data). You can check yours in Google Search Console under “Core Web Vitals”.
The most common causes of slowness
The majority of slow sites suffer from the same problems.
Images that are too heavy. A photo taken with a modern camera can weigh several megabytes. On an unoptimised site, it’s loaded as-is. A properly compressed image converted to WebP or AVIF can weigh ten times less for a visually identical result.
Low-end shared hosting. An overloaded server takes longer to respond to requests. TTFB (Time To First Byte) is often the primary cause of slowness, before page weight is even a factor.
Scripts loaded unnecessarily. Chat widgets, analytics tools, tracking scripts, social widgets — every third-party element added to a page has a loading-time cost. Many sites accumulate these without measuring their impact.
An overloaded CMS. WordPress with many plugins generates a lot of code, database queries and processing on every visit. A non-optimised theme can add several seconds of load time without the owner noticing.
No CDN cache. If your site is hosted on a single server in Germany or France, a visitor in Belgium waits for data to travel the network. A CDN (Content Delivery Network) serves your pages from the point nearest to the visitor.
Render-blocking JavaScript. Code loaded at the top of the page that delays the display of content. Solution: defer or async-load anything non-critical.
What a good performance score means
The reference tool for measuring a site’s speed is PageSpeed Insights, offered for free by Google. It gives a score from 0 to 100 and details the issues found.
- Score below 50 on mobile: the site has serious problems that drive away a significant share of visitors
- Between 50 and 89: improvements available, some heavily impact conversion
- From 90 upwards: the site is considered performant — this is the standard to aim for
The majority of WordPress sites with generic themes score in the 30–60 range on mobile. This is measurable, and it’s directly linked to the number of clients you’re losing every day.
The concrete cost of one extra second
A few figures documented by web giants:
- Amazon calculated that each additional second of load time cost 1% of revenue (worth several hundred million on their volume)
- Walmart: +2% conversion for each second saved
- BBC: 10% of visitors lost per second of delay
For a Luxembourg SME getting 100 visits a day with a 3% conversion rate, going from 4 seconds to 2 seconds can raise conversion to 4–5% — meaning 1–2 additional leads per day. Over a year, that’s dozens of extra quotes.
What changes when you build differently
At slash.lu, every site is built with Astro.js in static mode. Pages are generated once at build time and served directly from a CDN (Vercel Edge Network) — no server-side computation on every visit. Images are systematically converted to WebP/AVIF and resized according to the actual display size.
The typical result: a PageSpeed score between 95 and 100 on mobile, and a load time under one second on a normal connection. That’s what our clients Innovalux, AutoRachat and Tack obtained.
This isn’t a technical feat. It’s simply what happens when you treat performance as a starting constraint rather than a late-stage adjustment. It’s the founding principle behind our web design service .
How to check your site’s performance
- Go to pagespeed.web.dev
- Enter your URL and run the analysis
- Focus first on the mobile score — that’s where problems are typically most visible
- Check the “Real Experience Data” section: this is what Google uses for ranking
- Read the “Opportunities” listed at the bottom: these are prioritised concrete actions
If your score is below 70 on mobile, a significant portion of your visitors are leaving your site before they’ve even read your content. It’s a problem that can be diagnosed and fixed.
Where to start
If your site is slow, the first actions to consider:
- Image optimisation: compress and convert to WebP/AVIF (typical gain: 30-50% speed)
- Hosting: move from shared to VPS or static hosting with CDN
- Remove non-essential scripts: weigh each plugin against its real utility
- Enable caching: static assets (CSS, JS, images) with long TTL
- Lazy loading: images loaded only when they become visible on screen
These are measures that can have a quick impact without rebuilding the entire site.
If the problems run deeper — an overloaded CMS, an architecture not suited to mobile, old dependencies — rebuilding on a modern framework (Astro, Next.js, SvelteKit) is often the most effective solution in the medium term.
Going further
To understand how performance connects with local search rankings, read our article on how to dominate your area in 90 days through local SEO. And for the mobile angle specifically, see also why 70% of your clients view you on smartphone.
How we work at slash.lu
If you’d like us to look at your site and identify what’s slowing it down, let’s talk. We look at your situation, list the priority levers, and tell you honestly whether optimisation is enough or whether a rebuild is more cost-effective.
Let's talk about your situation. Book a call — no commitment, reply within 24h.
→ Going further: our web design service .