Can I run two 4k (3840x2160) displays at 60hz on a Macbook Pro 13" 2015
Assuming that you are using an Early 2015 MacBook Pro 13", it uses the Intel Iris 6100 chip.

From the review of the Intel Iris 6100 by NotebookCheck:


  All Broadwell GPUs support OpenCL 2.0 and DirectX 12 (FL 11_1). The video engine can now decode H.265 using both fixed function hardware as well as available GPU shaders. Up to three displays can be connected via DP 1.2/eDP 1.3 (max. 3840 x 2160 @ 60 Hz) or HDMI 1.4a (max. 3840 x 2160 @ 24 Hz). HDMI 2.0, however, is not supported.


The capability is there to support up to 3 displays with a max resolution of 3840x2160 @ 60Hz.

You connect it via mDP (mini Display Port) through the Thunderbolt 2 port.