A cloud provider is designing a new platform for serving large language models. They are debating between two primary design philosophies:

1. Standardized Fleet: Using only one model of the latest, most powerful processing units, which is expensive but ensures all hardware is identical.
2. Mixed Fleet: Using a combination of new and older, less powerful processing units, which is more cost-effective but results in a mix of hardware capabilities.

Analyze how the choice between these two fleet types interacts with the challenge of meeting strict, low-latency response time requirements for real-time applications. In your analysis, discuss the specific difficulties that arise when trying to achieve low latency in the 'Mixed Fleet' scenario compared to the 'Standardized Fleet' scenario.