If you're only clocking your CPU up to 4.2ghz, you don't need the D15. The Noctua HN-L9x65 would probably be more than enough for your CPU, both at home and when transporting, or even a Noctua NH-L9i. I can run my 22nm i5 at 4.6ghz using the low-profile NH-L9i and stay well below throttling temps.
There are other cheaper options that will work adequately, but most cheap coolers come with poor quality fans, which is why I tend to recommend people either use the stock cooler (which your CPU doesn't include), or go with something nice like a Noctua.