Here are the options to resolve your issue.
1st Option
Create an LVA asset class for your depreciation area 15 only.
Go to OAYZ and deactivate all areas other than area 15
2nd Option
You should create transaction type that will limit the posting in depreciation 15
When posting an acquisition for LVA asset, depreciation area 15, use the ttype.
Hope this resolves your issue.
Thanks!
jhero