it's definitely an upgrade it literally has DD Bass quality the only thing is that S15 is just too much Overpriced with atleast $150 otherwise it's am amazing IEM
Should I make a comparison video? In short vs MP145 with red filter, S15 is cleaner, tighter, more technically capable and resolving. If you use the silver nozzle, 145 will be more V shaped, lacking bass body, similarly less defined but more energetic treble.
S15 not worth it at all, sounds pretty much the same as my Artti T10 with less treble. My EW200 destroys it. For the price, not good. MP145 is the best IEM you can get. It's just perfect, except for the size but it's comfortable still.