Is it normal for a girl to have 15 sexual partners at 23?

I just started dating a girl I went to high school with about 3 months ago. We reconnected after five years apart and found out we were very much alike and both decided to give it shot. She told me that she had only been in one relationship and lost her virginity to the her first boyfriend at 21 during her second year of university. According to her the relationship lasted three years.

She later told me that the relationship with her first boyfriend was very tumultuous and left her emotionally drained. They constantly broke up and got back together over a course of three years.
My suspicions about whorish behavior arose after she lied about cheating to get back at her boyfriend. I asked a couple of times about it but she gave me false answers until she finally came clean.

Then she said that she had only slept with three guys including me but she always felt uncomfortable anytime issues of the past her came up. She adamantly stated that she has only been with three guys and I took her word for it .

Yesterday after an outing she said knew a hotel that both of us could relax and that a former male acquaintance knew the owners and it will be okay for both of us to lodge there to get some privacy. She was a bit coy to give information on this old acquaintance as she said she lost all contact with him

I found out I knew this guy she was talking about and found out both of them were still friends on Facebook even recently liking his profile picture. I probed further and found out she slept with him before. I told her I wanted her to be honest with me about everything .She then said that she had slept with 15 guys most of which happened with a year ago.

I was a bit disappointed because she lied about everything and it is hard for me to trust her now. Shes 24 now and in a span of three years after losing her virginity she's slept with 15 guys. Isn't it a bit worrisome?