I think you can get by with just the
C5! To help appreciate what follows, read
this document from Antennas Direct's site. Also keep in mind that the desired noise margin once we're done is +15. All your desired available stations have signals that are much stronger than that, which makes this much easier.
You have fairly strong network affiliates across a wide range of azimuth. Your two available NBC stations define this range: roughly 110 degrees to 320 degrees. No antenna can be uniformly sensitive across that entire range. However, by looking carefully, we can match antenna performance to the requirements presented by your TVFool report.
For VHF, you have stations roughly 110 and 210 degrees, a 100 degree spread. The station at 212 degrees has a noise margin of 54, so you don't need any antenna gain to capture it. The weakest station at 100 degrees has a noise margin of 9.9, so you would need about 5 dB of antenna gain for reliable results. NOTE: this is a second ABC station. If you don't care about it, then the next strongest station at that azimuth has a noise margin of 24, which doesn't need any antenna gain to be captured.
Look at page 3 of the document I linked to and you will find plots of the gain patterns for the C5 at VHF frequencies. Note that the antenna will still have +5 dB gain 25 degrees away from the center azimuth. From where the main beam crosses +5, rotate through the main beam 100 degrees and you'll see that the C5 has about -10 dB gain. That is plenty for the very strong stations, so you can set the C5 at 136 degrees and get what you want. (KLFY CBS, WAFB CBS, and WBRZ, ABC) Note that with this aim, we're getting close to a null for KLFY. A bit of tweaking to get it and WBRZ at the same time may be needed.
For UHF, you have stations at roughly 110, 160, 210, and 320 degrees. The weakest of these (discounting the low-powers and the second PBS) is WGMB, the second FOX affiliate, which has a noise margin of 24. To match the C5's UHF response, go to the last page of the pdf, equate the 0 azimuth to 136, then compare the antenna gains at the needed azimuths to the noise margins provided. You will see that, despite antenna gains as low as -10 in the needed directions, this is more than enough to receive a reliable signal.
You used 15 feet as the antenna height. Since you already have line-of-sight (LOS) to the transmitters you want, going higher will not improve the situation. All you need to ensure is that the antenna is not blocked to the front or back by local obstructions, like your house
Good luck.