I was taught the half gust factor trick so in the example quoted difference between "steady" speed and "gust speed" is 15 knots so add 7.5 knots. However that's approach speed and you'd be wise to come over the threshold at less than approach speed if you don't want to float forever in a Warrior. The little bit of extra momentum on the glide slope helps avoid too much corrective throttle and attitude for us less than skygod pilots whenit's gusty.
My similar Archer would in the conditions you describe fly base at 75 kts final at 70 (instead of 65) and still cross the threshold at 60 but I'd be ready for a (very) little blip of throttle to cushion the touch down if the wind drops at the last second.
In fact once set up on the final approach (visual) I don't really look at the clocks and dials I look at the picture in front of me and try keep it constant until I'm ready to close the throttle completely and land.