2.5'', 2.75'' and 3'' tie with 3-3.15'' lapel

You need to look at things in the full context. A 3" lapel on a 36S jacket might call for a different tie than the same lapel on a 48R jacket. Use your eye.

^This .... and even though the width of tie and the width of the lapel should be in the same ballpark, they do not have to be the identical down to the millimeter (for the readers in the US, North Korea and Liberia: 1 millimeter = ~0.04 inches). So, my guess is that 2.5-3 inch ties with a approximately 3 inch lapel should look fine.

3.5" ties work with 3" lapels, I'd be surprised if 2.5" ties didn't. 3" is a very versatile lapel width and tends to accomodate a fairly wide range of tie types. It's when one wears truly skinny lapels (or really broad ones) that a discrepancy is more noticeable.

Put it on and take a look. Your eyes will tell you more than I can (without seeing the outfit).