Say it straight or don't say it at all.
If a local business website feels slow on mobile, it is probably costing leads. Speed is not a technical vanity metric. It affects trust and action.
PNG files are massive compared to modern formats. A WebP image can be 12 to 14 times smaller at the same visual quality. If your site still uses PNGs, you are paying for that in load time and rankings.
A slow website costs you in two ways simultaneously: lower search rankings and worse conversion rates. Both of those hit revenue. Speed is not a technical nice-to-have. It is a business issue.