I have a TM-5402 M1 and an F15 and there is nothing between them in signal sensitivity. However when it comes to clearing pictures each one clears pictures that the other one does not even though they both scanned them in OK.
Its just my personal opinion but I think the F15 is overrated, it is half decent, but it is not an absolutely fantastic receiver. My F15 is for sale in the classifieds if anyone wants to buy it, that's how much I think of it, its just another receiver that I wish I had not bothered buying.
Rgds