it seems like every turbotax employee is adamant that I cannot depreciate my leasehold improvements
Probably because you're calling them "leasehold improvements" instead of "Qualified Improvement Property (QIP)" which is how it's addressed in the IRS Pubs.
I think your improvements would be more clearly classified as QIP (Qualified Improvement Property) which is depreciated over 15 years, or the terms of the lease to included projected renewals. The only thing I can find in IRS publication 946 is the definition of leasehold improvements. It says nothing about reporting them. But Qualified Improvement Property is addressed in the pub.
Additionally, the TTX program does have a selection for QIP and the default depreciation on that is 15 years as I would expect.
I suggest you take a l;ook at Pub 946 at https://www.irs.gov/pub/irs-pdf/p946.pdf and read all you can about QIP. Also, quit using the term "Leasehold Improvements" and start using "Qualified Improvement Property" once you make a determination that's what you have. You need to read the pubs, because not everything we think qualifies as QIP, actually does.
