Odd looking SWR

 

My 10m sweep

My Hustler 4BTV has now been up to 5 years and I was thinking it was due time to take it down and give it a good cleaning. Before I do that I wanted to take a baseline SWR of each band and see if the SWR changes after the cleaning. I used my NanoVNA to take the SWR readings and in my opinion, my 15m readings looked a bit odd. I have posted a sweep of 10m and then 15m and you can see the large spikes in the 15m readings. I am not sure why this is and I am searching for some input. 

 

15m sweep