
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given an arithmetic sequence ${a_n}$ with the sum of its first $n$ terms denoted as $S_n$. The first term $a_1 = 3$ and the sum of its first three terms $S_3 = 15$.
(I) Find the general term formula of the sequence ${a_n}$;
(II) Denote the sum of the first $n$ terms of the sequence $\{ \frac{1}{S_n}\}$ as $T_n$, find the minimum value of $T_n$.

Present the answer in LaTex format: \boxed{Your answer}
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