An 8GB M3 MacBook Air is officially compatible with macOS 27 Golden Gate.
Apple describes macOS 27 as including improvements to performance, stability, and responsiveness, but that does not establish how an 8GB M3 MacBook Air will perform compared with macOS 15.
High memory usage alone does not show that 8GB is causing the stuttering.
Memory pressure, swap activity, the applications being used, and available storage can all be relevant when investigating system responsiveness.
Apple recommends using Memory Pressure and Swap Used in Activity Monitor when evaluating memory use.
Use the Activity Monitor application and select View >> View All Processes. Identify the processes using the most CPU and Memory.
Available space on the internal SSD should also be checked. macOS uses the startup disk for system operations and, when necessary, virtual memory.
Therefore, unusually low free space is another factor worth investigating when a Mac is experiencing stuttering or general sluggishness.
It should not, however, be assumed to be the cause without checking how much space is actually available.
Because you have already erased and reinstalled the Mac, I would not upgrade specifically on the expectation that macOS 27 will resolve the problem.
Before upgrading, I would check Memory Pressure, Swap Used, the applications consuming the most memory, and the available space on the internal SSD while the problem is occurring.
If Memory Pressure remains green and there is ample free storage while the stuttering occurs, those observations would make insufficient RAM or storage less compelling explanations.
If Memory Pressure repeatedly rises while the problem occurs, or available storage is unusually low, those factors would warrant further investigation.
macOS 27 was released only recently, so reports from 8GB M3 owners are still relatively early and do not yet establish whether the new system is generally better, similar, or worse than macOS 15 on this configuration.
Apple's relevant guides are
Check if your Mac needs more RAM in Activity Monitor, View memory usage in Activity Monitor, and Free up storage space on Mac.
