B618 is a better choice, B715 is a popular modem-router because of the "poor offer" DIL in RBM (aggregates LTE2100MHz band, which in the case of Play in many locations increases this network usability).
On the B715 it does not aggregate LTE2600 + 2100 +1800 and LTE2600 + 2100 + 800, with aggregates LTE2600 + 1800 + 800 and LTE2100 + 1800 + 800, two LTE networks aggregates in all combinations. In Play, you have access to all 4 bands and in Orange up to 3 LTE bands? B618 does not aggregate LTE2600 + 2100, it has 4 internal antennas for MIMO4x4 but only two connectors for external antennas.
Modulation modulation ... and a clogged transmitter is still a problem ... B618 aggregates 2 frequencies and B517 3? is there a router that aggregates at least 3 supports 256-QAM mods and 4x4? I have 618 but I need 2 router I have an orange and an antennae call I have such an RSRQ signal: -11dB RSRP: -89dBm SINR: 2dB of course the router works with aggregation ... on the same mast is also play which has all frequencies. That's why I am so careful because in my area there are only a few and one radio operator that offers 10/2 transfer ... orange also walks 16/8 in the morning and in the evening 50/15 ...
Added after 3 [hours] 36 [minutes]:
Netgear Nighthawk M1 does this meet the above requirements?