does rotating proxy increase the difficulty to find your real IP?
No. Your "real IP" is either disclosed in some way, or it is not. If it is not, it does not matter how many proxies you pass through.
Multiple proxies may make more difficult to track your activity, i.e. establish that actions A and B were both performed by the same entity (for that, see fingerprinting, below).
It might be argued that the more proxies you use, the more likely that one of them will be compromised or misconfigured and will leak your address. In this case the likelihood is low because all proxies will probably be centrally managed.
On the other hand, by using cookies and fingerprinting (you may want to google "panopticlick"), it becomes possible to mark all of your connections as belonging to the same user, let's call him "UNKNOWN-1".
Now knowing that UNKNOWN-1 is using fourteen different servers, if they are distributed around the planet, it is possible, using timing techniques, to estimate the distance (both in hops and in kilometers) between UNKNOWN-1 and each of those servers, albeit with a possibly conspicuous error margin.
If the proxies don't employ time fudging techniques, and chances are that they don't, it becomes possible to restrict your location geographically. Your real IP is still unrevealed, but you're less anonymous than if you used a single proxy.
There are also much more complicated techniques that cross-check your timing data with real-time network traffic status ("Internet weather"). They require resources, time, and a lot of traffic from your host to some monitored facility (even a single website might do). For example if I have restricted your location to somewhere in Southern Europe, if your connections through the Amsterdam proxy begin lagging when the route from Amsterdam to GARR is hosed, and you stop lagging when service is restored, my confidence of you being in Italy increases greatly. At that point I start monitoring service levels for Italian providers...