PhD requires technology - is this something I will have to fund?
As a student, you should not be required to fund equipment purchases yourself.  Rather, it is your supervisor's responsibility to work with you to scope a project that is within the funding that they wish to allocate to it.  So if your supervisor wants to do a study with 15 people, your supervisor needs to have a sufficient budget to support it.  Otherwise, you might end up, say, doing your work in simulation instead, which is much cheaper but less convincing in its results.

Now, some students do buy small things themselves, especially if it is a low-cost "toy" that they want to play with themselves (e.g., a Raspberry Pi or a phone sensor pack) and they don't want to go through the delay and hassle of university purchasing.  That's an exception, however, and certainly not to be expected for a multi-user study.