I was initially going to leave this one for comment from the other forum members, however this question does bring up a potential concern.
First, to answer the question, Part 15 refers to any device that is capable of transmit and/or receive on radio frequencies, not just radios. It can be computers, tablets, garage door openers, modems, etc. If the question is specifically about transceivers, it pretty much covers any radio. For instance, a ham radio can be Part 15 type accepted and have a removeable antenna.
Part 90 radios certainly may have removeable antennas.
As for Part 95, whether or not the antenna is detachable depends on the individual radio service, referred to as subparts in the Code of Federal Requlations (CFR), as a number of radio services fall under Part 95, such as CB, FRS, GMRS and MURS. Each of those services is a subpart of Part 95.
For example, Subpart B is the Family Radio Service (FRS), Subpart D is CB, Subpart E is the General Mobile Radios Service (GMRS), etc.
Subpart B (FRS) states that FRS radios cannot have removeable antennas, but Subpart E (GMRS) does allow GMRS radios to have them.
The real concern for me isn’t the question itself. It’s the source of the query. I understand that the OP may represent a radio manufacturer or reseller in some way. If the question was merely posted to get a conversation going, that’s fine. However, it comes across as not knowing their own product. This is a question that anyone who manufactures, markets or sells radios in the US should already know before those radios are even made.
If I was visiting this forum and saw a radio manufacturer who was already actively selling radios labeled FCC Part 90 or Part 95 to the US market, and didn’t know what the FCC rules were for type accepting or selling those particular products in the US, I would be a little concerned about those radios.