From the case specifications, the MB will fit well with the Define R5, and the case can support the 140mm h115i too, but like your friend said the case is difficult to fit all items. I added the link for the same case with h110igt, that cooler size is similar to your h115i. https://i.imgur.com/1sDWC6H.jpg
A friend has the Define R4 and told me that ita was difficult to fit all items in the case. So I am wondering if I will make it put them all together. Note that I will install hydro h115i as well.
From the case specifications, the MB will fit well with the Define R5, and the case can support the 140mm h115i too, but like your friend said the case is difficult to fit all items. I added the link for the same case with h110igt, that cooler size is similar to your h115i. https://i.imgur.com/1sDWC6H.jpg