When you say connected to the testicle, do you mean directly or do you feel any "tubes?"
I would STRONGLY suggest you see your doctor or even better, a urologist - SOON.
Yes, there is a chance of testicular cancer - based upon your description. Don't panic, it is curable if caught in time.
Oh, don't frighten yourself by self-diagnosis a cancer. Yea, that's true that the most common symptom of testicular cancer is a lump or swelling in one of your testicles. But also a truth that most testicular lumps or swellings are not a sign of cancer. Research has shown that less than 4% of testicular lumps are cancerous. For example, varicoceles (swollen blood vessels) are a common cause of testicular lumps. (my nephew have been suffering from one before and later got treated by herbal medicine called diuretic andanti-inflammatory pill)
It is very important to visit your GP as soon as you notice any lump or swelling on your testicle, your GP will examine your testicles to help determine whether or not the lump is cancerous. Since you're only 15, i highly doubt that's a cancer problem, lol. I believe you'll be fine. Good luck!