Of course, this may or may not matter, depending on what documents you open.
If you only work with documents you created, then go ahead and keep on using version 7.5 until the end of time (or until you upgrade the computer).
If, on the other hand, you open documents received from the Internet, then no longer getting updates could create a security problem.
If possible, use something else (maybe a web app or something with no macro/scripting capabilities) to open Internet-retrieved documents, and reserve LibreOffice 7.5 for already-trusted documents (e.g. ones you created).