Will iMac 27" late 2015 be able to use Ventura?

at this time Apple is saying 2017 devices are as far back as the support will allow

about 3/4 the end of this page is a compatibility list.

macOS Ventura Preview - Apple

No, a 2015 has been moved to Vintage status and as has already been stated Apple has indicated a 2017 or later iMac is needed to run Ventura.