I think you'll find the 2152 is actually in the 11.5# weight range, but no matter...
If you are not fit enough to use a 2152 all day, you soon will be. If you complete the contract.
I understand and sympathize with your wish to use as light a saw as you can get away with. However, you don't want to spend all day 'waiting on the saw', either.
If this project has USDA oversight they may not LET you use a tophandle saw on the ground. Big brother is 'watching out for your safety'.
Maybe have a look at (at least) something like the echo 361p rearhandle before you buy.