I am sorry to see that you did not receive a reply. I installed the GTS last month and would love to do a TPMS upgrade. Please let me know if you get any information, or have any luck.
Upgraded to the GTS as well and loving the improvement

The lack of response probably means my post had too much information motor1
UPDATE: This information applies specifically to 2015 FLTRUSE owners wanting to retrofit the TPMS feature introduced in the 2016 FLTRUSE. Research indicated we needed wheel sensors, an updated BCM to receive the pressure signal and a means to display tire pressure as well as low pressure warnings.
BCM (Body Control Module: Was mostly having an issue identifying/ordering the correct BCM (41000341) but had an epiphany moment when I realized that the 41000341 BCM was included in the 41000087F Smart Security System Kit which also includes the newer FOB's.
WHEELS/8.3mm Sensors: Consulted the part number lists of the 2015 & 2016 FLTRUSE model years and determined the wheel part numbers are identical, i.e. since TP sensors were standard on the 2016 CVO Slicer wheels, our 2015 Slicer wheels should accommodate the sensors as well;
Tire pressure display and warnings: the 2015 CVO tachometer lacks the warning light present on the 2016+ models, but the 6.5GT or 6.5GTS head units will display a warning pop-up similar to the "low fuel" warning. Accordingly, I'll not bother ordering a 2016+ CVO gauge($) for a warning light. Of course both the GT/GTS head unit and BCM would need to be flashed by H-D to enable TPMS displays and the newer FOB's.
So, unless someone advises of a discrepancy in the above logic, I'm planning to place an order for the following:
• 2 each: 32700052 Chrome Wheel Valve-Sensors (32700096 if you wanted black);
• 1 each: 41000087F Smart Security System Kit;
Total cost for TPMS parts is approximately $450 Probably won't perform the installation until tire replacement ........so need the country to open up more to accommodate a few thousand miles of Road Tripping

In the meanwhile I'm hoping for some helpful confirmation feedback. NOTE: similar logic should apply for upgrading 2017 - 2019 model years except for the BCM requirement (which they already have) and the possibility of needing an adapter if their wheel's valve stem holes are 11.3mm.