Do you have any major concerns with the 58/15 LT's? Do you have multiple guitars with the 58/15 LT's?
If the answer is no to either, then why change? Can some changes in the settings of gear you have help with any issues you have? Personally I buy guitars because of the way they sound, feel, play and look - if any of those things are not quite right, I don't buy but that's my philosophy and not everyones. I own both a solid double cut 594 and a Hollowbody II - both with the 58/15 LT's fitted and both sound amazing to me. The 594 has the option to split the Pups whilst the HBii can add the Piezo in but I have no issues with either guitar.
Like you, I have a guitar with the 85/15's as well except mine are in the Custom 24. My PRS Special 22 Semi-Hollow has the 58/15 MT's and these both suit the pick-ups. In fact I can't think of any PRS in the current range that I think the PU's are perhaps slightly 'wrong' or could be better - no doubt PRS may find some way to better these as they continuously strive for perfection.
What helped me was hearing the story or knowing the history, where a 'guitar' was placed - not just in terms of features but also the era they are trying to evoke, what the 'spirit' of them was. Paul often talked about playing a 58 Les Paul for example and when he realised that none of the people had played a 58 LP, their only experience coming from re-issues and realising that the cost and rarity to find one that was 'good' would mean that none would ever get to play something like that, that's were the 594 was born but with modern PRS build quality and features like coil splitting and locking tuners. The Pattern Vintage neck and LT PU's were also introduced so knowing that the guitar was built evoke that spirit, you can see why those PU's work. Its similar to the Silver Sky and delivering a 63/64 Strat (albeit because that's what John Mayer wanted). That nailed that era and again cannot buy a 63/64 strat at that price with the consistency and quality so is much more accessible to all.
The Custom 22/24 guitars are more modern and why the 85/15's fit them well. I know not everyone wants a LP type to be more vintage sounding and want some different pups - each to their own and as its their instrument, their choice. There is the 'if it ain't broke...' but also there is the 'don't know until you try it' too. At least if you do try it, you can easily change it back if it doesn't work out for you. If you can't do it for yourself, the only thing you will lose is money - paying someone else to swap it out (and back again if you are not happy).
