As an auditor, you need to understand several aspects of IFRS 15 to effectively audit a company's application of the standard. Here are some key points to consider:

1. Understanding the Standard: Have a thorough understanding of the five-step revenue recognition model in IFRS 15 and the key concepts and principles in the standard. This includes understanding how to identify contracts, performance obligations, and how to measure and allocate transaction prices.
2. Management Judgements and Estimates: Be aware of the areas where management judgment and estimates are required, such as determining standalone selling prices, estimating variable consideration, and determining whether a performance obligation is satisfied over time or at a point in time. You need to challenge and test these estimates and judgements.
3. Understanding the Company's Business Model: Understand the entity's revenue streams and the terms and conditions of its contracts with customers. This will involve gaining an understanding of the business, its pricing strategies, and its contract negotiation processes.
4. Contract Review: Review sample contracts to understand how the company identifies contracts, performance obligations, and how it determines transaction price and allocates it to the performance obligations.
5. Internal Controls: Assess the design and implementation of internal controls over revenue recognition, especially in areas that require significant judgment or estimation.
6. Disclosures: Ensure that the company has provided sufficient disclosures as required by IFRS 15, to enable users of the financial statements to understand the nature, timing, amount, and uncertainty of revenue and cash flows from contracts with customers.
7. Comparative Information: Where applicable, evaluate the impact of any changes in revenue recognition on the comparative periods and the appropriateness of any restatements.
8. Transition Arrangements: If the company is transitioning to IFRS 15, understand the method of adoption chosen (full retrospective or modified retrospective) and assess the impact on the financial statements.

Remember, the primary objective of an auditor is to gain reasonable assurance that the financial statements as a whole are free from material misstatement, whether due to fraud or error. Hence, your focus should be on areas where there is a high risk of material misstatement in the context of revenue recognition.