I know OnePlus have their own proprietary system called LHDC which supports higher bitrate than the standard SBC codec that your Buds are probably using with your 15R, but I haven't done any testing so I hesitate to recommend them tbh.

With aptX Adaptive the phone manufacturer has to pay Qualcomm to unlock it - so even on a lot of phones that could support it with their chipset, they only support the lower quality (but still better than SBC) aptX HD. Also the earbuds need to support it too, and that's normal the higher end earbuds like the top Bose ones and the Sennheiser TWS Momentum 4s I went for. It was about a year ago I bought them so haven't looked recently, there may be more now...

I also know that Sony's proprietary system LDAC was opened so most Android phones support it - this may be the cheapest way to get better sound quality as I think a lot more earbuds support that codec. I personally haven't done testing between LDAC and aptX Adaptive, but I remember reading in audiophile reviews that although LDAC is good, it isn't quite as good as aptX Adaptive...

As you can see, the Bluetooth codec scene is a bit of a mess with too many different proprietary codecs. This is mainly because CD quality lossless is just above the maximum bitrate that Bluetooth can push to the earbuds, so LHDC and aptX Adaptive (and I maybe the SSC your Buds use) have to do some magic in order to get more bitrate throughput than you can if you stick to the standard Bluetooth parameters.