Welcome to the forum!
Sounds like it has a few issues there, hopefiully we'll get through them without too much bother.
The clutch is hydraulic, earlier models than yours sometimes had an issue with the thrust fork (the device that pushes the thrust bearing onto the back of the pressure plate to release the clutch). Checking fluids (and any possible expansion of the hydraulic line while it's in use - 2 people required) would be a good first step.
Boost control on yours should be electric, not vacuum so there's no control solenoid like the older models. Really easy to tell: there are three parts to the turbocharger:
* the impeller housing for the intake air to be compressed and sent to the engine
* the turbine housing for the exhaust gas to drive the turbocharger and send the exhaust out
* the vane actuator that sits at 90 degrees from the axis of the turbo, between the two other parts
The actuator will have either a vacuum hose - in which case you DO have a BCS, see below for testing - or an electrical connector, which Nissan did a recall on some of the models around 2014 for (and I can't be certain that the 2015 model wasn't covered in that recall). As far as I know the only way to test the electronic ones is to monitor the boost levels.
The vacuum ones are easier to test. There's a vacuum hose (inside diameter 3mm) that crosses over the top of the engine from the vacuum pump to the boost control solenoid (BCS). Disconnect this hose from the BCS and connect it directly to the turbocharger and take the car for a drive. If the BCS was faulty, the turbocharger should be hugely responsive (excessively so, since there's nothing regulating it, take care to not pop the air hoses off - take your foot off the accelerator slowly). If you still don't have a lot of turbo response, either there's a vacuum leak or there's something not quite right with the turbo.
Let's get that sorted then we'll look at the DPF issue.
