Oppo just unveiled the Reno15 and Reno15 Pro in China, and during the launch event for those two, the company also teased the Reno15c.
This will be the cheapest option of the bunch, and will arrive in December. Unfortunately, the company hasn’t shared any specs for the 15c, only showed the slide you can see below.

The design is clearly very similar to that of the other two members of the family, unsurprisingly. As it will be the cheapest of the three, expect the 15c to also be the lowest-end. We’ll let you know when we find out more about it.
Source (in Chinese)