What if (heaven forbid) the company folds, and I find myself looking for a new job? I will get low-balled by every company out there on the basis of my previous salary. In addition to that risk, I feel that they're essentially asking me to take a pay cut for the company, which wouldn't even be out of the question if I felt like it would be appreciated, but I don't think they see it that way. Lastly, we are a small company, but our overall costs run in the millions of dollars per year, and so even if the company is not doing well, I hardly think that a $15k salary bump for one employee is going to affect things very much.
First, I would just wait until you finish school. Looking for a job and going to school won't be fun.
Second, don't worry. Every time I switched jobs in my lifetime, I've gotten a significant pay bump in doing so. When you apply for the job, use market rates from salary.com and glassdoor.com in your area to determine what you should get based on your experience.