The USB blaster you linked to should work, though I have had issues with those cheaper ones.
Why would you want an LCD with 15khz support? The point of RetroTINK and/or C64 component is so that you don’t ever need such things. Keep your C64 component mod in 240p and just feed it to RetroTINK like that. On your RetroTINK I think you’re confused and passthrough mode is the one that does not work while line double does, that’s the case on many displays.