I'm confused about what the question is. Your Pages panel looks normal.
In the Pages panel menu, try turning on/off Allow Document Pages to Shuffle and Allow Selected Spread to Shuffle to see if you can get what you want. If that doesn't give you what you want, maybe you need to set up the document as single sided instead of facing pages (File > Document Setup), and then set up your master pages accordingly.
A possible change (I can't test in an earlier version of InDesign unfortunately, as not installed on my system), could be that if you create a 3-page master spread in InDesign, the 'Allow Select Spread to Shuffle' setting is automatically disabled.
Which would allow you to drag the master into the document and automatically create more island spreads (as your 13-15 pages). If you don't want that behaviour, you'd need to select the spread for which this shouldn't apply and as the previous poster mentions, enable the Allow Selected Spread to Shuffle option again for that spread.
Thank you thank you thank you both! It was the 'Allow Document Pages to Shuffle' which was on!