Standard protocol is to count polys, not vertices. I'm going to assume you have less polys than vertices since a poly needs a minimum of three vertices. That is a VERY small age to be getting lag in already. First two culprits to check are how you set up collision and whether or not you have run-time lighting in the age. I'm hypothesizing on what could possibly cause lag in an age that tiny and the only theory I can think of is:
1 - you have triangle mesh collision on everything, plus
2 - you have every material set to utilize in-game lighting, plus
3 - you have a waveset, plus
4 - you have shadows on your avatar, and maybe
5 - there's also something else animated on link-in
OR
6 - you have a 20 year old computer

Have you always had the lag or has it started recently? Can you do a trace back and determine when the lag started? Are you saving your builds in increments (a LOT of increments)?
Sorry that I have more questions than answers, but the only way to find a solution is to get to the root cause.