According to this https://meraki.cisco.com/lib/pdf/meraki_whitepaper_mx_sizing_guide.pdf
That MX450 supports 1000 concurrent VPN tunnels. So even if every one of your 150 branches had dual connections that would still only be 300 tunnels. Although I'd keep an eye on the utilization.
Adam R MS | CISSP, CISM, VCP, MCITP, CCNP, ITILv3, CMNO
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