MBP mid-2015 SSD is PCIe or ?

I assume you've already populated slots 5 and 6 with something that can't be moved to the PCH slot 4? In any case, assuming you're using

Although the PCIe GEN 3 slot should detect a GEN 2 controller and run as designed, this is not always the case Drives Dropping from the array- Known good

candy tower slot No No graphics card on the market will be noticeably impeded by a PCI-E slot You'd see 1-2% difference with the

can you use ddr5 in ddr4 slot PCIe slots feature the same pin layout and thus are forwards and backward-compatible However, a PCIe card slotted into a PCIe slot will