At this point it might be helpful if you gave us some more information on your PCa. I'm not sure what you mean about slow progress with your PSA score. You don't appear to be on a testosterone inhibitor, so are you talking about it going up or down?
For comparison, I'm 74, have a Gleason score of 9 and have had radiotherapy followed by HT [Zoladex]. Like you, I don't rate sexual performance as vital. What I've found with Zoladex is that while it does a great job of keeping my psa down post RT, it does have some undesirable side effects, both physical and mental, that I could well do without. If indeed castration would have the same effect it would not be a great deal of fun.
As others have suggested above, it might be worth trying out the injections first before you make your decision.
Responses to treatment vary between people so you might find a drug like Zoladex to be quite acceptable long term. Another factor here could be your current testosterone level. At 87 it might already be quite low so you might have less trouble adjusting to its disappearance than others who have a higher testosterone level.
Jules