Too many variables. Every home (building) is different. Ambient advertises 300 ft direct line of sight connectivity, but typical expected range is 100 to 150 feet. It may work out for you to try Ambient.
The 915 MHz and 433 MHz frequency difference is not enough to compare the two. There are other variables. For example Davis uses 915 MHz and goes 1000 Feet, and Acurite Atlas Elite (as advertised) will use 433 MHz and also go 1000 Feet. So it depends on the transmit power and the ability of the receiving end to fix on the signal depending on its receiving antenna.
In comparing cellular frequencies which are very different the lower the frequency the better the in-building penetration. That is why Verizon and AT&T hog up the more costly wireless real estate and have paid more for their spectrum in government frequency auctions. Also likewise when you compare WiFi that is available on 2.4 GHz and 5 GHz often people assume that the 5 GHz bandwidth is better because it is advertised as faster. But that is only true at closer range. How the 5 GHz channels have been set up they are wider so more data can be sent at any given moment. The 2.4 GHz band is lower in frequency and can transmit further and has better wall penetration and wall bounce capability, but much slower only because of the FCC limitation of the channels available and their width. 2.4 GHz can actually be better and faster at longer distance than the attenuation that rapidly occurs to a 5 GHz signal. That is why I set my WiFi SSID to be the same for 2.4 and 5 GHz and let the device decide which band to use.
It is therefore technically possible that 433 MHz is better for distance and wall penetration and wall bounce. But it really depends on all those other factors I mentioned. All things would need to be equal (antenna type, size, transmit power, and bandwidth use, channel width). You can't blindly just on paper compare 433 MHz with 915 MHz and make any determination as to if the Acurite using 433 MHz or the Ambient using 915 MHz is better.
In Europe Ambient's OEM manufacture Fine Offset and its clones use 433 MHz. For some reason Ambient doesn't use 433 MHz in the US and I don't know why that is. I've often heard said that it was because of FCC regulations. But if Acurite is able to use 433 MHz in the US, then I don't understand the logic in Ambient needing to use 915 MHz. I think it is possible that this was done deliberately to reduce gray market sales. As in if you have a 433 MHz station then it wouldn't work with 915 MHz ObserverIP and vise versa and would also work for limiting replacement parts.