Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Poll Source | Dates administered | Democrat: Brian Schweitzer | Republican: Roy Brown | Libertarian: Stan Jones | Lead Margin |
| --- | --- | --- | --- | --- | --- |
| Public Policy Polling | November 2, 2008 | 62% | 36% | not an option | 26.0 |
| Rasmussen Reports | October 1, 2008 | 56% | 41% | not an option | 15.0 |
| Rasmussen Reports | July 29, 2008 | 59% | 35% | 3% | 24.0 |
| Rasmussen Reports | June 30, 2008 | 61% | 32% | 3% | 29.0 |
| Mason Dixon/Lee Newspapers | May 19–21, 2008 | 55% | 30% | 2% | 25.0 |
| Mason Dixon/Lee Newspapers | December 17–19, 2007 | 55% | 30% | not an option | 15.0 |
Question:
What is the largest lead margin when Schweitzer has 55% and Jones is not an option?
Answer:
15.0