Ceiling fan and light on separate three way switches, code compliant?
You have a rather...neutral problem on your hands

In your diagram, the neutrals in the two inter-box cables are connected in parallel.  This can be interpreted as a violation of 300.3(B) and 310.10(H) regarding current-carrying conductors in parallel outside the same sheathe or raceway.

In practice, what will happen is the parallel neutrals will create a magnetic field between them, which will heat any ferrous metals in that field to at least some degree.  This can make for a bad day when it's a bit of junction box between two knockouts that's getting toasty inside your wall!

Fixing this might be actually rather easy, though. One option would be to use a 14-2-2 from the fan/light back to the switch -- this allows the fan and light to be wired to their own neutrals, although you'd probably have to modify your fan to bring the light's neutral out separately to do this.  In this case, the fan-travelers and fan-neutral are in one 14-3 between the switches, while the light-travelers and light-neutral are in the other 14-3.

Of course, if you can run a conduit or listed surface raceway between the two boxes, then you can simply pull in whatever wires you need provided the conduit fill isn't exceeded.  There are also multi-wire metal clad cables available (with 6 wires or even more) that could be applied here if a conduit run is impractical, although you'd need to order them through an electrical supply house.